In general, vibration originating from machines or other sources is most often undesirable and detrimental. For example, vibration in a precision machining tool may lead to faults and imperfections in work pieces produced on the tool. The vibration also may be transmitted through the floor and disrupt other tools. Additionally, the noise generally associated with machine vibration may be disruptive to workers.
Various methods and devices exist to reduce undesirable vibrations and may be generally categorized as vibration isolators or suppressors. Typically, vibration isolation devices operate locally to reduce transmissibility, wherein transmissibility is typically defined as the ratio of the transmitted force to the disturbing force. As such, vibration isolation devices are particularly suitable for reducing discrete and transient vibrations. For example, various reflexive and absorptive material, such as rubber, cork, foam and the like, may be placed in connective elements of a stamping machine, such as the stamping table and legs, to isolate the discrete vibrations associated with the stamping action of the machine.
In contrast, vibration suppression devices typically operate globally to suppress vibration. As such, vibration suppression devices are particularly suitable for reducing cyclic vibrations or vibrations which may be difficult to isolate to a particular element of a machine. For example, the motor of a machine generates cyclic vibrations. Rather than attempting to isolate the vibration transmitted through various connective elements of the machine, the entire machine may be mounted on a vibration suppression base. While the vibration suppression base may reduce the global vibration generated by the machine, local transmission of vibration may not be altered. In fact, certain vibration suppression devices may actually amplify local transmission of vibration.
Vibration mitigation devices may be categorized further as active or passive devices. Typically, active devices incorporate a feedback system which detects the amplitude and/or frequency of the disrupting vibration and responds accordingly to reduce or eliminate the vibration. TD Therefore, active devices are capable of broadband reduction of vibration. However, the complexity and cost of typical active devices often make them impractical for many applications.
In contrast, passive devices are typically mechanical devices which generally use various spring elements and damping elements to reduce or eliminate vibrations. However, conventional passive devices generally operate to reduce vibrations only in a fairly narrow bandwidth. Additionally, certain materials used in conventional passive devices, such as rubber and lubricating fluid, may be inappropriate for use in certain environments, such as clean room environments.
A spring damper device is one conventional passive vibration suppression device which is described in various mechanical textbooks and handbooks. In a spring damper device, a spring element and a damper element reduce vibration by removing the energy of a vibrating system through the damper element. However, the spring damper device typically operates at a narrow bandwidth determined by the stiffness of the spring element and the damper coefficient of the damper element. Typically, vibrations outside of this narrow preset bandwidth will not be effectively reduced. In fact, vibrations at certain frequencies will often produce increased responses with a peak response occurring when the frequency of the vibration is equal to the natural frequency of the spring damper system. Consequently, a spring damper device must often be precisely calibrated to match the frequency of the vibrating system.
In another conventional device, a spring element is used in combination with a beam-column element to reduce the transmission of vibration. See U.S. Pat. No. 5,178,357, issued on January 1993, to Platus and related U.S. Pat. No. 5,549,270, issued on August 1996, to Platus et al. More particularly, a spring and a beam-column are calibrated such that one element has a positive stiffness and the other element has an equal negative stiffness. In this manner, an object is supported with net-zero effective stiffness. However, a spring and beam-column pair is required for each axis to be isolated from vibration and each spring and beam-column pair must be precisely calibrated to achieve a net-zero effective stiffness in each axis. As such, this method is fairly complicated and difficult to calibrate and adjust. Additionally, as the requisite negative and positive stiffness are achieve through two separate elements, if one element wears at a rate different than that of the other, their stiffness will no longer match and a net-zero effective stiffness will not be achieved.